Laser-initiated vacuum plasma shutters using a dielectric aperture for retropulse isolation

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Abstract
It is demonstrated that sintered LiF spatial-filter apertures may be used in a vacuum environment of 10−6 Torr as laser-initiated plasma shutters for retropulse isolation in high-energy laser fusion systems. In the experimental data presented, a 1.1-ns duration pulsed CO2 laser at 10.6-μm wavelength with an energy of 3.0 J is used for plasma initiation. A chopped cw CO2 laser tuned to 9.6 μm is used as a probe laser in determining the time the plasma blocks transmission of a CO2 laser beam. Both the 10.6- and the 9.6-μm transmission were measured as a function of pulsed laser fluence on the aperture edge, up to 240 J/cm2. Blocking times in excess of 1.0 μs were observed for an aperture diameter of 800 μm, for a Gaussian beam with a diameter of 1.2 mm determined at the 1/e2 intensity points.